Aggarwal Neha, Mishra Divya Kumari, Srivastava Shivalee, Mathews Runcie Paul
Birbal Sahni Institute of Palaeosciences, 53, University Road, Lucknow 226007, India.
ACS Omega. 2025 Feb 11;10(7):6707-6720. doi: 10.1021/acsomega.4c08281. eCollection 2025 Feb 25.
This study conducts a comprehensive palynofacies and geochemical analysis to characterize organic matter (OM) in shale samples from the Godavari Basin. Palynofacies analysis identified three types of organic matter under transmitted light: translucent organic matter (TrOM), comprising palynomorphs, structured phytoclasts, and degraded organic matter; and two types of opaque phytoclasts/charcoal (CH), distinguished as palaeofire-induced (PAL-CH) and oxidized (OX-CH). The multifaceted approach is applied through Raman spectroscopy, Rock-Eval, and Fourier transform infrared spectroscopy (FTIR) to assess organic carbon's thermal evolution and structural integrity required to substantiate the palynological evidence on microcharcoal. The intensity ratio (ID/IG) ranged from 0.20 to 0.47, indicating varying impacts of thermal events on carbon structures. Higher ID/IG ratios corresponded with samples affected by palaeofires. Additionally, D-FWHM and G-FWHM parameters were analyzed, revealing larger D-FWHM values in thermally matured samples, indicating greater disorder in the carbon structure. The D-FWHM/G-FWHM ratio, exceeding unity, suggested significant structural shifts toward disordered carbon domains. Consequently, the presence of overmaturation of organic matter ranging from 411 to 609 °C indicates the alteration of organic matter due to the impact of heat causing the removal of hydrogen from the samples. FTIR spectroscopy suggests the presence of aromatic and aliphatic deformation due to thermal maturation. This integrated approach combining palaeofire history, Raman spectroscopy, and geochemical analysis provides valuable insights into the palaeofire history and structural evolution of charcoal in the Godavari Basin shales.
本研究对哥达瓦里盆地页岩样品中的有机质（OM）进行了全面的孢粉相和地球化学分析。孢粉相分析在透射光下识别出三种类型的有机质：半透明有机质（TrOM），包括孢粉体、结构化植物碎屑和降解有机质；以及两种类型的不透明植物碎屑/木炭（CH），区分为古火诱导型（PAL-CH）和氧化型（OX-CH）。通过拉曼光谱、岩石热解和傅里叶变换红外光谱（FTIR）应用多方面方法，以评估有机碳的热演化和结构完整性，从而证实关于微木炭的孢粉学证据。强度比（ID/IG）范围为0.20至0.47，表明热事件对碳结构的影响各异。较高的ID/IG比值对应受古火影响的样品。此外，对D-FWHM和G-FWHM参数进行了分析，结果显示热成熟样品中的D-FWHM值更大，表明碳结构的无序程度更高。D-FWHM/G-FWHM比值超过1，表明向无序碳域发生了显著的结构转变。因此，有机质存在411至609℃的过成熟现象，这表明由于热影响导致样品中氢的去除，有机质发生了改变。FTIR光谱表明由于热成熟存在芳香族和脂肪族变形。这种结合古火历史、拉曼光谱和地球化学分析的综合方法，为哥达瓦里盆地页岩中古火历史和木炭的结构演化提供了有价值的见解。
